The invention relates to a method for producing a lever arm with a tip for a scanning microscope. The invention also resides in such a lever arm.
The patent publication EP 0 619 872 B1 and DE 44 37 306 C 2disclose lever arms for scanning microscopes, which include a piezo-resistive resistance integrated in the lever arm. The deflections of the lever arm change the resistance. The resistance change is a measure for the deflection. According to DE 44 37 306 C2, the piezo-resistive resistance is part of a MOSFET.
For the manufacturer of such a lever arm, the C-MOS technique may be employed, by way of which the resistances are implanted in chips as follows.
On a wafer consisting of a single-crystal silicon with a thin oxide layer on its surface a photo lacquer is deposited. The photo lacquer is partially exposed to light in a well-defined manner by using a mask and is developed and, in this way, partially removed. A window is formed in the enamel layer. The location the expanse (size) of the window corresponds to the location and the size of the piezo-resistive resistance to be implanted in the wafer. Subsequently, a beam of suitable ions such as boron--arsenic--or phosphorus ions is directed onto the lacquer layer including the window. In this way, ions are implanted in the wafer through the window in a spatially limited manner. Then the photo-lacquer is completely removed by solvents such as acetone.
In order to provide the resistance with electric contacts, a new photo lacquer layer is then applied. Windows are formed in the photo lacquer layer at locations where the resistance is to be connected to electric conductors. Through the windows for example boron ions are implanted. The dose is now substantially greater than the dose employed during the first implantation operation. The high dose is required for establishing a resistive contact with the implanted resistance. Otherwise, a semiconductor diode could be formed which is not desired. The enamel is again fully removed. A temperature treatment at temperatures of about 1050.degree. C. is performed. The crystal structure damaged by the exposure to the ion radiation is cured in this way. After curing, the resistance implanted below the oxide layer has the desired piezo-resistive properties.
A new enamel layer is then applied. Windows are formed in the varnish at the predetermined contact locations. The oxide layer is removed in the area of the windows by chemical etching using hydrofluoric acid. Then the photo enamel is completely removed by solvents such as acetone. A metal layer is then applied over a large area. A photo lacquer varnish is deposited on the metal layer--a window is formed in the varnish. The location and size of the window are so selected that the metal layer can be separated, through the window, into two electrically separated areas. After separation of the metal layer into two areas, the contact locations are no longer electrically interconnected. By ion radiation etching, the metal is removed in the area of the window so that two isolated areas are formed. Then the photo lacquer is completely removed by solvents such as acetone.
The desired piezo-resistive resistance is now present in the wafer. A voltage can be applied to the implanted resistance by way of the metallic areas (conductor paths).
Subsequently, the wafer must be treated (for example, by etching) in such a way that it is shaped and sized properly for a lever arm of a scanning microscope. Finally, the tip is cemented to the lever arm by hand.
The method for the manufacture of a piezo-resistive resistance in a wafer as described before is relatively inexpensive. However, the manual cementing of the tip makes the process substantially more expensive.
With the method described above, it is impossible to implant a piezo-resistive resistance in a lever arm-like wafer, which is already provided with a tip.
With this method, the tip as well as the fragile lever arm would be destroyed. It is for example, impossible to protect the tip by means of a photo lacquer since the lacquer layer comes loose at the tip. Subsequent ion beam etching would therefore damage the tip.
The tip is furthermore damaged by oxidation at temperatures of 1000.degree. C. and more. Also, thermal tensions could destroy the fragile tip.
For technical reasons, a lever arm etched out of a conventional wafer has a relatively uneven surface. Photo lacquer layers cannot be applied with uniform thickness on an uneven surface. Areas with such thin photo lacquer layers that they cannot withstand requirements can therefore not be avoided. For example, very thin areas can be damaged by the subsequent ion irradiation to such an extent that the lacquer cannot be removed by exposure to light and development or by a solvent.
It is the object of the present invention to provide a comparably inexpensive method of manufacturing a lever arm of the type referred to above as well as such a lever arm.